1. Field of the Invention
This invention relates to copper alloys for electric and electronic devices and to a method for producing the same. More particularly, it relates to copper alloys for electric and electronic devices which have excellent resistance to the peeling of coated tin plating or tin alloy plating and to a method for producing the alloys.
2. Description of the Prior Art
In general, high strength and high conductivity copper alloys are suitable for use in the manufacture of electric and electronic devices. In particular, Cu-Ni-Si alloys satisfy characteristic requirements of alloys for use in the manufacture of such articles. Alloys for electric and electronic devices are manufactured with an applied tin plating or solder plating, said plating being made of a tin alloy. A problem with conventional tin alloy platings is that they peel or crack, which obviously lessens the reliability of the plated products. In view of this problem, alloy plated electric and electronic devices are subjected, for example, to a high temperature storage test after soldering, in which the soldered alloys are heated under the conditions of 150.degree. C. for 500 hrs in air to determine the resistance of tin and solder platings to peeling. In spite of their high strength and high conductivity, the above-mentioned Cu-Ni-Si alloys possess the drawback that when they are subjected to the high temperature storage test after soldering, the solder is liable to peel. Thus, such alloys have heretofore experienced only limited use in the manufacture of electric and electronic devices.
In order to overcome the disadvantages of the conventional alloys, studies have been made in which a variety of elements have been added to Cu-Ni-Si alloys. As a results, it has now been found that incorporation of Zn with or without Cr is effective in improving the peeling resistance of such alloys. Moreover, it has also been found, as the result of X-ray diffraction analysis, that in Cu-Ni-Si alloys, precipitation of Ni.sub.2 Si in large amounts contributes to improvement in the peeling resistance of the applied solder. Moreover, it has been ascertained that the annealing temperature of 400.degree.-550.degree. C. after cold working is the point at which Ni.sub.2 Si precipitates at the highest level. The annealing time used was in the range of 5 minutes-4 hours.
Because Cu-Ni-Si alloys are of the precipitation hardening type, their cold workability is greatly influenced by the quenching conditions after hot working. Accordingly, quenching conditions have been investigated in order to improve productivity and to achieve stabilization of quality, with the result that it has been found that the quenching temperature should be over 600.degree. C. with a cooling rate over 15.degree. C. per second.